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Inducktion

Wed Jun 01 2011, 11:19PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

SO, I had an idea in my head, and put it to work. It's a pretty simple 555 timer circuit, with a mosfet gate drive IC (to help the bugger charge the gates, since the 555 can only source 200 mA), a low pass filter, and the mosfet itself! The speaker is pretty large, input voltage is actually around 41 volts (I wasn't really thinking about voltage at the moment, so disregard what I said in the video) and the audio quality is amazing! I need to figure out how to increase the output... I'm thinking either push pull, or a full bridge, but with a push pull that requires a V- rail. but with a full bridge that requires a bit more circuitry to drive the gates....

I'll try to get working on a stereo version of this baby, and post a schematic soon.

Mattski

Thu Jun 02 2011, 04:23AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

It looks nice and simple, but sounds nice!

There was a big inductor on an E-core ferrite I saw, was that part of the output filter or was there an inductor on the board? What frequency were you running at? Also I'm a little curious what the exact schematic is, I've used a 555 in a plasma speaker, but the 555 was just generating a sawtooth wave which was fed into a comparator along with an audio signal to generate the PWM signal. Are you getting the PWM completely from the 555?

Mycologist

Thu Jun 02 2011, 03:10PM

Registered Member #2413 Joined: Sat Oct 03 2009, 08:27PM
Location: Essex, UK
Posts: 22

I agree with Mattski, this looks pretty impressive!
I've been looking to build some sort of decent audio amp for a while now, after getting sick of trying to properly manage heat from class A. This might be just what I'm looking for...

Steve Conner

Thu Jun 02 2011, 05:41PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yay, you got it working! How much distortion do you reckon it is putting out?

Inducktion

Thu Jun 02 2011, 08:31PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

I don't honestly know, actually. But, I will say this; I'm almost positive it's a current amplifier, and I need to make it so it does a better job at it (the speaker was actually roughly the same loudness with just the ipod hooked up to it, to my disappointment) I.E. more bass, because I'm almost positive right now it's amplifying very little. I'll fix it with a full bridge or half bridge of mosfets. (
And to Mattski, that inductor is for an IH I'm working on. It's not connected in any way to the amplifier. All of the PWM is being done by the little 555.

Goodchild

Fri Jun 03 2011, 07:31AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

2 ways to get more volume out of a class D more duty and more voltage.

In your video I only saw one MOSFET? Where is the other one hiding?

Nice work, you are getting some fantastic sound quality for just a 555. Is there nothing the humble 555 can't do?

MRacerxdl

Fri Jun 03 2011, 01:31PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

I think he only uses one mosfet to switch. It can work too, but less power than an half-bridge.

Inductiktion, have you thinked about using a P and N channel mosfet to do a bridge? It can be simple to you drive them without an GDT. IRF540 and IRF9540 can support 40V and can switch about 20A. It maybe good for you amplifier.

Anyways, the sound quality is great, gratz! :D

Inducktion

Fri Jun 03 2011, 04:26PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Full bridge time!

Goodchild

Fri Jun 03 2011, 05:02PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

MRacerxdl wrote ...

I think he only uses one mosfet to switch. It can work too, but less power than an half-bridge.

Inductiktion, have you thinked about using a P and N channel mosfet to do a bridge? It can be simple to you drive them without an GDT. IRF540 and IRF9540 can support 40V and can switch about 20A. It maybe good for you amplifier.

Anyways, the sound quality is great, gratz! :D

Well umm no it can't really work with one MOSFET. With a class D amp with no audio coming out the square wave is centered at 50% duty. When you create a sine wave you have to bring it into is positive cycle (highside MOSFET) and then into it's negative cycle (lowside MOSFET) with the zero cross at 50% duty.

Without the lowside MOSFET you have no way to make the other half of the sine wave and therefor you don't have a class D amp. With one MOSFET you made something more like a buck converter, assuming you used a diode on the low side. If this is what you made then it's no wonder your not getting much amplification.

A buck doesn't have near the same transient response as a class D amp. It can bring the voltage up fast but when it comes to bringing it back down it's going to take it's sweet time because it has to wait for the load to bring down the voltage.

Inducktion

Fri Jun 03 2011, 08:09PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Mm. I plan on making it a half bridge first, see how it works, how hot etc...

Hopefully it'll get a lot louder and better sounding than before.

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